Burglar alarm triggered by breaking of a magnetic circuit

ABSTRACT

A burglar alarm for use on a window in which the alarm is triggered by breaking of a magnetic circuit across the window. The magnetic circuit is defined by a pair of movable bar magnets carried on opposite sides of the window. One bar magnet is carried by a window screen or other movable member which when displaced carries it away from the window to break the magnetic circuit. The other bar magnet then moves to close an electrical alarm circuit.

[22] Filed:

United States Patent Callaghan [s41 BURGLAR ALARM TRIGGERED BY BREAKINGOF A MAGNETIC CIRCUIT [72] Inventor: James I. Callaghan, 11229 Camaril-10 St., North Hollywood, Calif. 91602 i Oct. 12, 1970 [2]] Appl. No.:79,832

52 us. 01. .l ....340/274, 49/13, zoo/61.84,

' 340/273 51 1111. c1. ..G08b 13/08 [58] Field of Search...340/274,273', 174 PM;

[56] References Cited UNITED STATES PATENTS 3,539,741 11/1970 Volandm,ZOO/61.62

11 1' 3,706,090 1451' Dec. 12, 1972- Qualheim ..200/61 .62

2,877,361 3/1959 Chase ..340/274 700,812 5/1902 Peyton ..335/2053,281,735 10/ l 966 Blumish ..335/207 Primary Examiner-John w. CaldwellAssistant Examiner-Glen R. Swann, lll Attorney-Nilsson, Robbins, Wills &Berliner ABSTRACT A burglar alarm for use on a window inwhich the alarmis triggered by breaking of a magnetic circuit across the window. Themagnetic circuit is defined by a pair of movable bar magnets carried onopposite sides of the window. One barmagnet is carried by a windowscreen or other movable member which when displaced carries it away fromthe window to break the magnetic circuit. The other bar magnet thenmoves to close an electrical alarm circuit.

17 Claims, 13 Drawing Figures PA'TENTED nu: 12 I972 SHEET 1 UF 2INVENTOR. 56 Cmmsw/v pmminnmzmz 3.706.090

SHEU 2 BF 2 INVEN'i'OR- dimes Cmmemq/v FIELD OF THE INVENTION The fieldof art to which the invention pertains includes the field of burglaralarms, particularly sound generating alarms.

BACKGROUND AND SUMMARY OF THE INVENTION The present invention provides alow cost, compact, self-contained burglar alarm unit which can beutilized on any window to provide a tamper proof alarm. The unit canoperate on batteries and the alarm generating components can beinstalled entirely on the inside of a window.

In accordance with this invention, a burglar alarm is provided in whichthe components define a magnetic circuit across a window, or the like,whereby upon breaking the circuit an alarm is triggered. Specifically,an alarm unit is disposed on the inside of the window and includes amagnet which cooperates with a second magnet on the opposite side of thewindow. The second magnet can be carried by a movable member such as awindow frame or a flat sheet of plexiglass or other transparent memberwhich acts as a barrier obstructing access to the window. The magnetscooperate to define a magnetic circuit and movement of the barrierresults in displacement of the second magnet to break the magneticcircuit.

The magnet on the inside of the window is disposed at an alarm setposition. A signal generating circuit cooperates with this magnet so asto energize a signal generator when the magnet is moved to an alarmposition. The magnet is continuously urged to the alarm position eitherby the force of gravity or by attraction to paramagnetic or magneticmaterial disposed at the alarm position. In a particular embodiment, thealarm circuit includes spaced contacts at the alarm position definingthe circuit as open and the magnet when displaced to that positionbridges the spaced contracts to thereby close the alarm circuit andtrigger the alarm. In another embodiment, the alarm circuit includes aswitch, such as a micro-switch which is spring loaded to close thesignal generator circuit but carried by the first magnet against theforce of the spring at the alarm set position so as to open the signalgenerator circuit. Upon breaking of the magnetic circuit, the firstmagnet moves away from the alarm set position, by gravity or otherwise,allowing the switch to close the signal generator circuit therebytriggering the alarm.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view ofa window incorporating a burglar alarm in accordance with thisinvention;

FIG. 2 is a cross-sectional view taken on line 2-2 of FIG. 1, in thedirection of the arrows;

FIG. 3 is a perspective view of a particular alarm unit shown open andpartially broken away;

FIGS. la-care schematic representations of the manner of operation ofthe burglar alarm unit of FIG.

FIG. 5 is a front elevational view of an alternative system utilizing aburglar alarm of this invention;

FIG. 6 is a cross-sectional view taken on line 6-6 of FIG. 5, in thedirection of the arrows;

FIG. 7 is a view similar to that of FIG. 6 but in a displaced positionwherein the alarm is triggered;

FIG. 8 is a schematic, perspective view, partially broken away, of aportion of an alternative alarm embodiment of this invention;

FIG. 9 is a schematic, perspective view, partially broken away, of aportion of another alternative alarm embodiment of this invention;

FIG. 10 is a schematic, cross-sectional view of still anotheralternative alarm embodiment of this invention; and

FIG. 11 is a perspective view of a connector which can be utilized inaccordance with an embodiment of the invention.

DETAILED DESCRIPTION As required, detailed illustrative embodiments ofthe invention are disclosed herein. However, it is to be understood thatthese embodiments merely exemplify the invention which may take manyforms radically different from the specific illustrative embodimentsdisclosed. Therefore, specific structural and functional details are notto be interpreted as limiting, but merely as a basis for the claimswhich define the scope of the invention. Somewhat in this regard, theillustrative embodiments herein comprise self-contained alarms operatingoff batteries. However, it is to be emphasized that the constructionherein is readily adaptable to the utilization of line current such ashousehold current. Furthermore, the embodiments disclosed utilize asound generator as an alarm signal, but the concepts herein areapplicable to visual alarms and to remotely signaling alarms.

Referring now to FIGS. 1 and 2, there is illustrated one manner ofutilization of an alarm unit 10 in accordance with the presentinvention. There is illustrated a window 12 secured within its sash 14which also carries a window screen 16 in its frame 18. A flat, rigidtransparent sheet 20 of plexiglass, or the like is carried centrally ofthe window screen 16 by means of a pair of oppositely disposed springs22 and 24 clamped to side members 26 and 28 of the screen frame 18 andto opposite side edges 30 and 32 of the plexiglass sheet 20. A barmagnet 34, which can be encased in plastic, is secured centrally of theplexiglass sheet 20, by adhesive or the like, so as to abut thewindowpane 12 when the window screen 16 is in its normal position. Thealarm unit 10 is carried on the other side of the windowpane 12 so as toeffect a magnetic circuit with the bar magnet 34, as will hereinafter bedescribed in more detail.

The alarm unit 10 is completely self-contained in that it includes asource of current and a sound generator and is responsive to a break inthe magnetic circuit to generate a loud sound to signal such a break.The magnetic circuit is broken by displacement of the bar magnet 34which occurs by a movement of the plexiglass sheet 20, such as byattempting to remove or cut the window screen 16. The result is that anattempt to burglarize by entering the window 12 is foiled by thetriggering of the alarm unit 10.

Referring now to FIG. 3, the unit-10 is illustrated in more detail. Thealarm unit 10 includes a plastic case 36 having two halves 38 and 40opening on a hinge 42 along its bottom edge and closing by means ofmatingly engageable clasp halves 44 and 46. The alarm unit includes athree volt horn 48 which is serially connected over the line 50 to apair of penlight batteries 52 and 54, interconnected by a line 56. Theborn 48 is connected over the line 58 to an electrically conductivestrip 60 and the penlight battery 54 is connected over a line 62 toanother electrically conductive strip 64 spaced from the first mentionedstrip 60. Referring briefly to FIG. 4a, each electrically conductivestrip 60 and 64 is supported via electrical insulation 66, such asrubber or the like, on a bar 68 of paramagneticmaterial. The strips 60and 64 are formed of nonmagnetic material, such as copper, aluminum,brass, or the like. The bar 68 may be ferromagnetic and made of iron,steel or the like; alternatively, it may be a bar magnet, e. g.constructed of Alnico metal.

The foregoing components are contained in'one-half 38 of the case 36,the other half 40 being empty except for a loosely contained bar magnet70 which is supported by the lower edge 72 of the case half 40. The barmagnet 70 is of Alnico metal of rectangular shape and of a lengthsufficient to bridge the spaced conductive strips 60 and 64. With thecase halves 38 and 40 closed, the bar magnet 70 would be magneticallydrawn to the case half 38 by means of the bar 68 of paramagnetic ormagnetic material. In use, however, the unit 10 is disposed with the barmagnet 70 opposite and aligned with the aforementioned bar magnet 34(FIG. 2) on the opposite side of the windowpane 12. The bar magnet 70 isthus held spaced from the conductive strips 60 and 64, albeitcontinuously urged toward the strips 60 and 64 as a result of thepresence of the paramagnetic or magnet bar 68.

Referring to both FIGS. 2 and 3, the alarm unit 10 is positioned so thatthe case half 40, containing the bar magnet 70, is facing the windowpane12 and is secured to the windowpane 12 by means of double sided adhesivestrips 74, or the like. Initially, to set the alarm, the unit 10 ispositioned with the case halves 38 and 40 opened and the bar magnet 70manually disposed into magnetic engagement with the bar magnet 34.Thereafter, the case 36 is closed and the alarm is set.

Referring additionally to FIG. 4, the manner of operation of the unit 10is schematically illustrated. As shown in FIG. 4a, a magnetic circuit iseffected between the bar magnets 34 and 70 whereby the bar magnet 70 issecured in an alarm set position spaced from the electrical conductingstrips 60 and 64. Referring to FIG. 4b, upon movement outwardly of theoutside bar magnet 34, as indicated by the arrow 76, the magneticcircuit is broken and the inside bar magnet 70 is drawn by attraction tothe paramagnetic or magnetic bar 68, as indicated by the arrows 78 toabut the electrically conductive strips 60 and 64. The bar magnet 70thus bridges the strips 60 and 64 to close the alarm circuit, therebyenergizing the 3-volt-horn 48. The horn is selected so as to generate apiercing sound, warning the occupants of the building that entrance hasbeen attempted and thwarting the burglary by giving clear inwith themagnetic bar 34. Alternatively, the bar 68 and adjacent material of theinner case half 38 can be formed with aligned openings 80 and 82 throughwhich is thrust a thin rod 84, as indicated by the arrow 86 to push theinner bar magnet 70 against the case half 40 in alignment with theoutside bar magnet 34.

It will be appreciated that the outside magnet 34 can be replaced by abar of paramagnetic material which has sufficient attraction for theinternal bar magnet 70 so asto function in the manner'described.Alternatively, the internal bar magnet 70 can be replaced by a'bar ofparamagnetic material provided the bar 68 supporting the spacedconductive strips 60 and 64 is constructed of magnetic material. Otherchanges and modifications can be madeconsistent with the foregoingconcepts. It will also be appreciated that when the alarm is not used itis in a quiescent state and does not draw current from the batteries 52and 54. It is only when an alarm is generated that current is drawn withthe result that the alarm unit 10 has a lifetime as long as the storagelife of the batteries. Periodic testing is easily accommodated by simplyopening the case and momentarily bridging the strips 60 and 64 with thebar magnet 70. In place of the 3-v.olt horn 48, one could utilize anysignaling means in that the lines and 58 leading to the horn 48 caninstead lead to any signaling device, on the premises or remote.

Referring now to FIGS. 5-7, a modification of the alarm system isillustrated. In this embodiment, the window 86 is not provided with awindow screen but is protected by a large sheet 88 of plexiglass or ofheavy screen material, as desired. The sheet 88 substantially covers thewindow 86 and is supported at its upper corners only by means of springs90 and 92 securing the upper comers to the window frame 94. The sheet 88thus hangs downwardly in front of the window 86. A bar magnet 96 ispivotally secured by means of a linkage 98 to a coupling volt 100centrally through the sheet 88. An alarm unit 102, identical to thealarm unit 10 of FIGS. 1-4, is secured to the opposite side of thewindowpane 86 so that its internal bar magnet is aligned with theexternal magnet 96. When the sheet 88 is moved away from the window 86,the bar magnet 98 is caused, by the linkage 96, to drop downwardly, notonly breaking the magnetic circuit, but thereby making replacement ofthe bar magnet 96 a difficult procedure. In the arrangement depicted inFIGS. 1 and 2, it might be possible to turn off the alarm by realigningthe external bar magnet 34 and jostling the windowpane 12 to I draw theinternal bar magnet 70 back into magnetic endication to the burglar thathis presence has been degagement with the external bar magnet 34. In thearrangement illustrated in FIGS. 5-7, such an attempt is made much moredifficult and generally would require the use of a long rod or the liketo hold the external bar magnet 96 up against the window, makingrealignment by jostling more unlikely.

Referring now to FIG. 8, there is illustrated an alternative embodiment.The alarm unit 104 is contained within a plastic case 106 which cannotbe snapped open as the case 36 depicted in FIG. 3. A pair ofelectrically conductive strips 108 and 110 are secured, by adhesive, orotherwise, against the rear wall 112 of the case and are connected vialines 114 and 116 to an alarm (not shown) in a manner similar to thearrangement depicted in FIG. 3. In this embodiment, the electrically.conductive strips are constructed of paramagnetic material, such as tin,so as to magnetically attract a bar magnet 118 movably disposed on thefront wall 120.

The bar magnet 118 is pivotally secured in the case by means of a hinge122 which allows the bar magnet 118 to pivot into bridging engagementwith the electrically conductive strips 108 and 110. In operation, whenan external magnet such as the bar magnet 34 or 96, as previouslydescribed, is placed in proximity to the front wall 120 in alignmentwith the forward position of the bar magnet 118, it secures the barmagnet 118 in an upright position spaced from the conductive strips 108and 110. Upon breaking of that magnetic circuit by removal of theexternal bar magnet 34 or 96, the bar magnet 1 18 is then attracted tothe electrically conductive strips 108 and 110 and pivots, as shown bythe arrow, into bridging engagement with the strips 108 and 110 tothereby close the alarm circuit, signaling the fact that the externalbar magnet 34 or 96 has been displaced.

To return the bar magnet 118 to its original position, the external barmagnet 34 or 96 is realigned in its alarm set position and a shaftsimilar to the shaft 84 depicted in FIG. 4c is inserted within anopening 124 defined through the rear case wall 112 until engagement withthe bar magnet 1 18 whereupon the shaft and magnet 118 can be pushedforward until the magnet 118 is in its upright position.

As further modification to the alarm unit 104 of FIG. 8, a spring can belocated between the bar magnet 118 and front case wall 120 urging thebar magnet 118 to an alarm position, the force of the spring beinginsufficient to overcome the magnetic attraction between the bar magnet118 and the external bar magnet 34 or 96. In this case, the electricallyconductive strips 108 and 110 can be made of non-magnetic material, suchas copper, etc.

Referring now to FIG. 9, another alternative embodiment is illustratedin which an alarm unit 126 is provided in the form of a closed case 128of plastic or the like. Spaced electrically conductive strips 130 and132 are secured to the rear case wall 134 and a bar magnet 136 isloosely disposed within the case 128. The bar magnet 136 is shapedrectangularly and is of such dimension as to be prevented from rotatingwithin the case 128. Thus the case 128 can be jostled and vibratedwithout significant change in the relative position of the bar magnet136 within the case 128.

In this embodiment the electrically conductive strips 130 and 132 are ofnonmagnetic material such as copper and the like but a plate 138 ofmagnetic or paramagnetic material is pivotally connected by a hinge 140to the top wall 142 of the case 128. The plate 138 can thus bepositioned adjacent the conductive strips 130 and 132 but insulatedtherefrom by the rear case wall 134 and attract the internal bar magnet136 when the external bar magnet 34 or 96 is removed. When this occurs,the electrically conductive strips 130 and 132 are bridged by the barmagnet 136, closing the alarm circuit. In this embodiment, the alarmcircuit is disposed exteriorly of the case 128 as indicated by the lines144 and 146 leading from the conductive strips 130 and 132 via openingssuch as 148 formed in the bottom case wall 150. The alarm circuit can besimilar to the circuit depicted in the unit of FIG. 3, or the lines 144and 146 can lead to a remote signaling device.

In operation, the magnetic or paramagnetic plate 138 is raised, asindicated by the arrow, and the unit 126 mounted, via adhesive strips152 to a window to be protected in a manner similar to the arrangementillustrated in FIGS. 1 and 2 or FIGS. 5-7. After alignment andcompletion of a magnetic circuit with an external bar magnet 34 or 96,the plate 138 is swung into contact with the rear case wall 134 so as tothereby continuously urge the internal bar magnet 136 to a rearward,alarm position, but resisted by the force of the external bar magnet 34or 96. Upon removal of the external bar magnet 34 or 96, the internalbar magnet 136 is propelled across the case 128 into bridging contactwith the conductive strips and 132, closing the alarm circuit. To resetthe alarm, the plate 138 is raised and the external bar magnet 34 or 96is replaced drawing the internal bar magnet 136 back into its alarm setposition.

Referring now to FIG. 10, there is illustrated still another alternativeembodiment of this invention in which an alarm unit 154 is providedwhich incorporates a microswitch 156 to close the circuit between a setof batteries 158 and a low voltage horn 160. The unit 154 includes acase 162 having a rear wall 164 formed with an opening to accommodatethe horn and defining a compartment 168 for the batteries 158. Themicroswitch 156 is spring loaded to close the alarm circuit but, whendisposed in an alarm set position, has its button 170 depressed againstthe force of its spring 172 to open the alarm circuit. The microswitch156 is carried by an aluminum support member 174 which is pivotallysecured at its bottom end by a hinge 176 internally of the case 162 soas to pivot toward the rear case wall 164.

The case 162 is open at its front end and is positioned against awindowpane 178. A bar magnet is secured to the forward surface of thesupport member 174 and the microswitch 156 is so positioned with respectto the magnet 180 that its button 170 is depressed by the windowpane 178when the magnet 180 abuts the windowpane 178.

In operation, the alarm unit 154 is situated with its open frontconfronting the windowpane 178 and its internal magnet 180 against thewindow pane 178 thereby opening the circuit on the microswitch as abovedescribed. An external bar magnet 182 is secured to a window screen 184by means of a bolt 186 and is magnetically aligned with the internal barmagnet 180 so as to define a magnetic circuit therewith and bias thesupport member 174 to an alarm set position. Upon removal of theexternal bar magnet 182, the internal bar magnet 180 is pulledrearwardly and downwardly by the force of gravity, releasing the springloaded microswitch button 170, thereby closing the alarm circuit tosound the horn 170 indicating an intrusion attempt.

Referring now to FIG. 11, there is illustrated an alternative method ofsecuring an external bar magnet 188 to a window screen 190 withoutrequiring bolts or a barrier sheet. The bar magnet 188 is secured at itsouter surface 192 to a bracket 194 which is formed with a channel 196 ofU-shaped cross section. The bracket channel 196 is designed to fitwithin the window screen frame channel 198, and, in turn, tightlyreceive the window screen frame 200. By such means, the barmagnet 188can be disposed against the window, between the window and screen 190 sothat when the screen 190 is removed it carries the magnet 188 out ofmagnetic engagement with the alarm unit on the other side of the window.

I claim 1. A burglar alarm comprising, in combination:

an alarm signal generator;

a first magnetically attractable member movable between spaced positionsof alarm set and alarm and continuously urged to said alarm position;

a second magnetically attractable member disposed in spaced proximity tosaid alarm set position;

at least one of said first and second members being magnetic, said firstand second members cooperating to define a first magnetic circuit atsaid alarm set position whereby to maintain said first member at saidalarm set position, said first and second members being relativelymovable whereby to break said first magnetic circuit releasing saidfirst member to move to said alarm position; and

circuit means connected to said signal generator comprising electricalcontacts, spaced from one another and fromsaid first member at saidalarm set position, defining said circuit as open, said first membereffecting electrical contact and bridging of said spaced contacts whensaid first member is moved to said alarm position thereby closing saidcircuit.

2. The invention according to claim 1 in which said first and secondmembers are both magnetic.

3. The invention according to claim 1 in which said spaced contacts arenonmagnetic.

4. A burglar alarm comprising, in combination;

an alarm signal generator;

a first magnetically attractable member movable between spaced positionsof alarm set and alarm;

a second magnetically attractable member disposed in spaced proximity tosaid alarm position;

at least one of said first and second members being magnetic, said firstand second members cooperating to define a first magnetic circuit atsaid alarm set position whereby to maintain said first member at saidalarm set position;

a third, magnetically attractive, member in proximity to said alarmposition, at least one of said first and third members being magnetic,said first and third members cooperating to define a second magneticcircuit at said alarm position and thereby continuously urge said firstmember to said alarm position whereby upon breaking of said firstmagnetic circuit said first member is magnetically drawn to said thirdmember; and

circuit means connected to said signal generator and cooperating withsaid first movable member for energizing said signal generator when saidfirst movable member is at said alarm position;

said first and second members being relatively movable to break saidfirst magnetic circuit whereby said first member is moved by saidcontinuously urging means to said alarm position.

5. A burglar alarm comprising, in combination:

an alarm signal generator;

a first magnetically attractable member movable between spaced positionsof alarm set and alarm, said alarm position being spaced below saidalarm set position whereby said first member is continuously urged tosaid alarm position by the force of gravity;

a second magnetically attractable member disposed in spaced proximity tosaid alarm set position;

at least one of said first and second members being magnetic, said firstand second members cooperating to define a first magnetic circuit atsaid alarm set position to maintain said first member at said alarm setposition, said first and second members being relatively movable tobreak said first magnetic circuit releasing said first member to move tosaid alarm position; and i circuit means connected to said signalgenerator and cooperating with said first movable member for energizingsaid signal generator when said first movable member is at said alarmposition.

6. A burglar alarm comprising, in combination:

an alarm signal generator;

a first magnetic member movable between spaced positions of alarm setand alarm and continuously urged to said alarm position;

a second magnetic member cooperating with said first magnetic member todefine a magnetic circuit at said alarm set position to maintain saidfirst magnetic member at said alarm set position, said first and secondmagnetic members being relatively movable to break said first magneticcircuit releasing said first magnetic member to move to said alarmposition; and

circuit means connected to said signal generator comprising electricalcontacts, spaced from one another and from said first magnetic member atsaid alarm set position, defining said circuit as open, said firstmagnetic member contacting and bridging said spaced contacts when movedto said alarm position to close said circuit.

7. The invention according to claim 6 including a third magnetic memberspaced further than said electrical contacts from said first magneticmember and disposed to continuously urge said first magnetic member tosaid alarm position.

8. A burglar alarm comprising, in combination:

an alarm signal generator;

a first magnetic member movable between spaced positions of alarm setand alarm;

a second magnetic member;

said first and second magnetic members cooperating to define a magneticcircuit at said alarm set position to maintain said first member at saidalarm set position; and

means for cooperating with said first magnetic member to define a secondmagnetic circuit at said alarm position and thereby continuously urgesaid first magnetic member to said alarm position whereby upon breakingof said first magnetic circuit said first magnetic member ismagnetically drawn to said means, said means comprising circuit meansconnectedto said signal generator and cooperating with said firstmagnetic member for energizing said signal generator when said firstmember is at said alarm position;

said first and second members being relatively movable to break saidfirst magnetic circuit whereby said first member is moved by saidcontinuously urging means to said alarm position.

9. The invention according to claim 8 in which said 10. The inventionaccording to claim 8 in which said means additionally comprises a thirdmagnetic member in proximity to said alarm position.

11. A burglar alarm comprising, in combination:

an alarm signal generator;

a first magnetic member movable between spaced positions of alarm setand alarm, said alarm position being spaced below said alarm setposition whereby said first member is continuously urged to said alarmposition by the force of gravity;

a second magnetic member cooperating with said first magnetic member todefine a first magnetic circuit at saidalarm set position to maintainsaid first magnetic member at said alarm set position, said first andsecond members being relatively movable to break said first magneticcircuit and release said first member to move to said alarm position;and

circuit means connected to said signal generator and cooperating withsaid first magnetic member for energizing said signal generator whensaid first magnetic member is at said alarm position.

12. A burglar alarm, comprising:

an alarm signal generator;

a housing having spaced front and rear walls;

a first magnetically attractable member between said front and rearhousing walls, spaced from one thereof and movable between spacedpositions of alarm adjacent said one wall and alarm set adjacent thewall opposite said one wall;

a second magnetically attractable member disposed externally of saidhousing front wall, at least one of said first and second members beingmagnetic, said first and second members cooperating to define a firstmagnetic circuit at said alarm set position whereby to maintain saidfirst member at said alarm set position;

magnetically attractive means in said housing adjacent said oppositewall for cooperating with said first magnetic member to define a secondmagnetic circuit at said alarm position and thereby continuously urgesaid first magnetic member to said alarm position whereby upon breakingof said first magnetic circuit said first member is magnetically drawnto said means, said means comprising circuit means connected to saidsignal generator and cooperating with said first member for energizingsaid signal generator when said first member is at said alarm position;

said first and second members are both magnetic.

. The invention according to claim 2 in which said alarm position isadjacent said rear wall.

15. A burglar alarm system, comprising:

a glass window;

a window cover movably disposed adjacent one side of said glass windowand covering substantially all of the area of said glass window on saidone side;

a first magnetically attractable member on a side of said glass windowopposite said first side and occupying a first minor portion only of theregion of said glass window on said opposite window side;

a second magnetically attractable member on said window cover adjacentsaid first window side and occupying a second minor portion only of theregion of said window cover, said first and second minor portions atleast overlapping;

at least one of said first and second members being magnetic, said firstand second members cooperating to define a magnetic circuit;

alarm means on said opposite window side responsive to a break in saidmagnetic circuit whereby to generate an alarm signal; and

means for connecting said second member to said window cover formovement therewith whereby movement of said window cover effects a breakin said magnetic circuit.

16. The invention according to claim 15 wherein said window covercomprises a window screen having screen material defining said secondminor portion.

17. A burglar alarm system, comprising:

a glass window;

a flat transparent member movably disposed adjacent one side of saidwindow;

a first magnetically attractable member on a side of said windowopposite said first side and occupying a first minor portion only of theregion of said glass window on said opposite window side;

a second magnetically attractable member on said first window side andoccupying a second minor portion only of the region of said secondwindow side, said first and second minor portions at least overlapping;

at least one of said first and second members being magnetic, said firstand second members cooperating to define a magnetic circuit;

alarm means on said opposite window side responsive to a break in saidmagnetic circuit whereby to generate an alarm signal; and

means for connecting said second member to said transparent member formovement therewith whereby movement of said transparent member effects abreak in said magnetic circuit.

1. A burglar alarm comprising, in combination: an alarm signalgenerator; a first magnetically attractable member movable betweenspaced positions of alarm set and alarm and continuously urged to saidalarm position; a second magnetically attractable member disposed inspaced proximity to said alarm set position; at least one of said firstand second members being magnetic, said first and second memberscooperating to define a first magnetic circuit at said alarm setposition whereby to maintain said first member at said alarm setposition, said first and second members being relatively movable wherebyto break said first magnetic circuit releasing said first member to moveto said alarm position; and circuit means connected to said signalgenerator comprising electrical contacts, spaced from one another andfrom said first member at said alarm set position, defining said circuitas open, said first member effecting electrical contact and bridging ofsaid spaced contacts when said first member is moved to said alarmposition thereby closing said circuit.
 2. The invention according toclaim 1 in which said first and second members are both magnetic.
 3. Theinvention according to claim 1 in which said spaced contacts arenonmagnetic.
 4. A burglar alarm comprising, in combination; an alarmsignal generator; a first magnetically attractable member movablebetween spaced positions of alarm set and alarm; a second magneticallyattractable member disposed in spaced proximity to said alarm position;at least one of said first and second members being magnetic, said firstand second members cooperating to define a first magnetic circuit atsaid alarm set position whereby to maintain said first member at saidalarm set position; a third, magnetically attractive, member inproximity to said alarm position, at least one of said first and thirdmembers being magnetic, said first and third members cooperating todefine a second magnetic circuit at said alarm position and therebycontinuously urge said first member to said alarm position whereby uponbreaking of said first magnetic circuit said first member ismagnetically drawn to said third member; and circuit means connected tosaid signal generator and cooperating with said first movable member forenergizing said signal generator when said first movable member is atsaid alarm position; said first and second members being relativelymovable to break said first magnetic circuit whereby said first memberis moved by said continuously urging means to said alarm position.
 5. Aburglar alarm comprising, in combination: an alarm signal generator; afirst magnetically attractAble member movable between spaced positionsof alarm set and alarm, said alarm position being spaced below saidalarm set position whereby said first member is continuously urged tosaid alarm position by the force of gravity; a second magneticallyattractable member disposed in spaced proximity to said alarm setposition; at least one of said first and second members being magnetic,said first and second members cooperating to define a first magneticcircuit at said alarm set position to maintain said first member at saidalarm set position, said first and second members being relativelymovable to break said first magnetic circuit releasing said first memberto move to said alarm position; and circuit means connected to saidsignal generator and cooperating with said first movable member forenergizing said signal generator when said first movable member is atsaid alarm position.
 6. A burglar alarm comprising, in combination: analarm signal generator; a first magnetic member movable between spacedpositions of alarm set and alarm and continuously urged to said alarmposition; a second magnetic member cooperating with said first magneticmember to define a magnetic circuit at said alarm set position tomaintain said first magnetic member at said alarm set position, saidfirst and second magnetic members being relatively movable to break saidfirst magnetic circuit releasing said first magnetic member to move tosaid alarm position; and circuit means connected to said signalgenerator comprising electrical contacts, spaced from one another andfrom said first magnetic member at said alarm set position, definingsaid circuit as open, said first magnetic member contacting and bridgingsaid spaced contacts when moved to said alarm position to close saidcircuit.
 7. The invention according to claim 6 including a thirdmagnetic member spaced further than said electrical contacts from saidfirst magnetic member and disposed to continuously urge said firstmagnetic member to said alarm position.
 8. A burglar alarm comprising,in combination: an alarm signal generator; a first magnetic membermovable between spaced positions of alarm set and alarm; a secondmagnetic member; said first and second magnetic members cooperating todefine a magnetic circuit at said alarm set position to maintain saidfirst member at said alarm set position; and means for cooperating withsaid first magnetic member to define a second magnetic circuit at saidalarm position and thereby continuously urge said first magnetic memberto said alarm position whereby upon breaking of said first magneticcircuit said first magnetic member is magnetically drawn to said means,said means comprising circuit means connected to said signal generatorand cooperating with said first magnetic member for energizing saidsignal generator when said first member is at said alarm position; saidfirst and second members being relatively movable to break said firstmagnetic circuit whereby said first member is moved by said continuouslyurging means to said alarm position.
 9. The invention according to claim8 in which said circuit means comprises a switch having a spring whichloads the switch to close said signal generator circuit, said switchbeing carried by said first member against the force of its spring atsaid alarm set position whereby to open said signal generator circuit.10. The invention according to claim 8 in which said means additionallycomprises a third magnetic member in proximity to said alarm position.11. A burglar alarm comprising, in combination: an alarm signalgenerator; a first magnetic member movable between spaced positions ofalarm set and alarm, said alarm position being spaced below said alarmset position whereby said first member is continuously urged to saidalarm position by the force of gravity; a second magnetic membercooperating with said first magnetic member to define a first magneticcircuit At said alarm set position to maintain said first magneticmember at said alarm set position, said first and second members beingrelatively movable to break said first magnetic circuit and release saidfirst member to move to said alarm position; and circuit means connectedto said signal generator and cooperating with said first magnetic memberfor energizing said signal generator when said first magnetic member isat said alarm position.
 12. A burglar alarm, comprising: an alarm signalgenerator; a housing having spaced front and rear walls; a firstmagnetically attractable member between said front and rear housingwalls, spaced from one thereof and movable between spaced positions ofalarm adjacent said one wall and alarm set adjacent the wall oppositesaid one wall; a second magnetically attractable member disposedexternally of said housing front wall, at least one of said first andsecond members being magnetic, said first and second members cooperatingto define a first magnetic circuit at said alarm set position whereby tomaintain said first member at said alarm set position; magneticallyattractive means in said housing adjacent said opposite wall forcooperating with said first magnetic member to define a second magneticcircuit at said alarm position and thereby continuously urge said firstmagnetic member to said alarm position whereby upon breaking of saidfirst magnetic circuit said first member is magnetically drawn to saidmeans, said means comprising circuit means connected to said signalgenerator and cooperating with said first member for energizing saidsignal generator when said first member is at said alarm position; saidsecond member being movable respective said housing front wall to breaksaid first magnetic circuit whereby said first member is moved by saidcontinuously urging means to said alarm position.
 13. The inventionaccording to claim 12 in which said first and second members are bothmagnetic.
 14. The invention according to claim 12 in which said alarmposition is adjacent said rear wall.
 15. A burglar alarm system,comprising: a glass window; a window cover movably disposed adjacent oneside of said glass window and covering substantially all of the area ofsaid glass window on said one side; a first magnetically attractablemember on a side of said glass window opposite said first side andoccupying a first minor portion only of the region of said glass windowon said opposite window side; a second magnetically attractable memberon said window cover adjacent said first window side and occupying asecond minor portion only of the region of said window cover, said firstand second minor portions at least overlapping; at least one of saidfirst and second members being magnetic, said first and second memberscooperating to define a magnetic circuit; alarm means on said oppositewindow side responsive to a break in said magnetic circuit whereby togenerate an alarm signal; and means for connecting said second member tosaid window cover for movement therewith whereby movement of said windowcover effects a break in said magnetic circuit.
 16. The inventionaccording to claim 15 wherein said window cover comprises a windowscreen having screen material defining said second minor portion.
 17. Aburglar alarm system, comprising: a glass window; a flat transparentmember movably disposed adjacent one side of said window; a firstmagnetically attractable member on a side of said window opposite saidfirst side and occupying a first minor portion only of the region ofsaid glass window on said opposite window side; a second magneticallyattractable member on said first window side and occupying a secondminor portion only of the region of said second window side, said firstand second minor portions at least overlapping; at least one of saidfirst and second members being magnetic, said first and second memberscooperating to define a magnetic circuit; alarm means on said oppositewindow side responsive to a break in said magnetic circuit whereby togenerate an alarm signal; and means for connecting said second member tosaid transparent member for movement therewith whereby movement of saidtransparent member effects a break in said magnetic circuit.